Comets and X-rays

17 Dec 2019

At ... telescopes around the world have been focussed on Comet Borisov, the apparent interstellar visitor. It is moving so fast it has not been captured by our Sun, yet still sports a tail of dust and debris.


At ... physicists claim to have solved the riddle of comets emitting X-rays. When comets travel through the solar system they interact with solar radiation, the solar wind, and the solar magnetic field. This induces a visible atmosphere around the comet (the coma) and the observed cometary tail. In some cases it also produces X-rays.

The authors of the study in Nature Physics (see ) did an experiment  by firing a laser beam on to a plastic foil, which exploded, causing a stream of electrons and ions to be expelled - creating a high speed flow of plasma (just like the solar wind). This plasma flow then impacted onto a solid sphere (a laboratory version of the comet) and electrons heated up to around one million degrees as a result of plasma turbulence. These hot electrons were responsible for emitting X-rays, we are told (but only in the presence of a magnetic field). Note also the laboratory comet was represented by a solid sphere. An experiment rather than a model simulation. Good.